Gwildor is a member of the Thenurians, a dwarf-like race of people. He is known throughout Eternia as a famous locksmith and inventor, and is notable mainly for his greatest creation: The Cosmic Key, a mechanical device with the ability to transport its holder to any place throughout space and time.

Gwildor was introduced into the mythology with his appearance in the 1987 live action film starring Dolph Lundgren. Played by Billy Barty, he was created specially for the movie to as a substitute for Orko,whose design was too complex for the studio to produce in live action with its limited budget. Frederick S. Clarke explains that Gwildor was "reportedly a stand-in for Orko...In the series Orko has no feet or legs and is always seen floating or flying, a difficult concept to film live..."[2]

As Cinefantastique reveals, veteran "midget actor Billy Barty plays Gwildor, an innocent locksmith/inventor thrown into the adventure when an invention he creates inadvertently gives Skeletor his power."[3] Thus, Gwildor's role in the movie is key to the central plot. He is introduced into the film when rescued by He-Man from Skeletor's soldiers. He then explains how he was tricked by Skeletor's sidekick Evil-Lyn into giving his prize creation The Cosmic Key to the forces of evil, and thus allowing them to enter Castle Grayskull and take over Eternia. As the unwitting cause of Grayskull's defeat, Gwildor endeavors to help He-Man overcome Skeletor by using a prototype Cosmic Key. When the heroes find themselves overwhelmed by Skeletor's army, Gwildor uses the Cosmic Key to help them escape, and the heroes are transported to Earth, leaving Gwildor faced with the task of finding the correct programming on the Key to transport them back before Skeletor gains the power of the universe.

Gwildor is presented as absent-minded and quite bumbling, but also wise, intelligent and good-hearted, with little fear. His Cosmic Key, meanwhile, is a complex device with numerous switches and buttons, which can be used to programme sonic waves, sounds, music and light patterns which serves to transport its users to the location of their choice.

In earlier drafts of the movie's script, Gwildor's character was slightly different. He was initially described as being even smaller and unable to walk long distances, meaning he had to be carried on Man-At-Arms' back for most of the story. He also had a fearful side to his character similar to that normally associated with the character of Cringer, and frequently becoming scared easily and cowering away from danger.

After the release of the movie, Gwildor was incorporated into the toy line with his own action figure, complete with Cosmic Key. A life-size Cosmic Key was also planned by Mattel, but the toy line was cancelled before it could be made.

He appears in the accompanying mini-comic "The Cosmic Key", which once again puts Gwildor and his creation in the spotlight, but this comic has no continuity with the movie, telling a radically different story of how He-Man came to meet Gwildor, instead having him summoned by The Sorceress to aid He-Man against an evil force.

Gwildor and the Cosmic Key also appear in numerous comics published after the movie, including those by Marvel Comics and various European comic series.

In January 2011, a new version of the Cosmic Key was released in the Masters of the Universe: Classics toyline. The Cosmic Key came with "Preternia Disguise He-Man", and was detailed to look like the version shown in the movie (with a few minor differences). A new Gwildor action figure is planned for release, but no date has been given at this time.